SQL query to return all records from current month in ASP.Net using C#

If i want show only this month isn't like this or different ?

string constr = ConfigurationManager.ConnectionStrings["kankonConnectionString"].ConnectionString;
using (SqlConnection con = new SqlConnection(constr))
{
    using (SqlCommand cmd = new SqlCommand())
    {
        string sql = "SELECT * FROM Table_special";
        if (!string.IsNullOrEmpty(civilid.Text.Trim()))
        {
            sql += " WHERE civilsp LIKE @civilsp + '%' ";
            sql += "  AND (CONVERT(DATETIME,datesp2) >= DATEADD(MONTH, -1, GETDATE()))";
            cmd.Parameters.AddWithValue("@civilsp", civilid.Text.Trim());
        }
        cmd.CommandText = sql;
        cmd.Connection = con;
        using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
        {
            DataTable dt = new DataTable();
            sda.Fill(dt);
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }
}